(1) Field of the Invention
The invention relates to an image display apparatus, and especially relates to an image display apparatus having a projection unit therein.
(2) Description of the Prior Art
Generally, slim television (TV) is able to be classified into three categories: plasma TV, LCD TV, and inner projection TV, popularly called rear projection TV, which employs an internal projection unit to produce an image. Normally, the projection unit used in the inner projection TV includes a bulb, a condenser, a digital micro-mirror device (DMD), and a projecting lens. The imaging formation of the projection unit is processed as following sequences: firstly, a light beam, which from the bulb is converged by the condenser, projects on the digital micro-mirror device (DMD); secondly, the light beam is reflected by the micro mirrors of the digital micro-mirror device (DMD) as an image beam; and finally, the image beam passes through the projecting lens to cast on associated faceplate to display a corresponding image.
Please refer to FIGS. 1A and 1B for the front and side elevations respectively showing an internal structure of a conventional inner projection television (TV) 100. The conventional inner projection TV 100 includes a projection unit 110, a folding mirror 120, a curve mirror 130, a plane mirror 140, and a screen 150. The projection unit 110 projects the image beam on the folding mirror 120 for being reflected to the curve mirror 130. By the curve mirror 130, the image beam is reflected to the plane mirror 140 at the rear side of the inner projection TV 100. Afterward the plane mirror 140 directly reflects the image beam to the screen 150 at the front side of the inner projection TV 100 for being viewed by the viewers.
Please refer to FIG. 2 for a pictorial view showing an internal component configuration of the conventional inner projection TV 100. In FIG. 2, the screen 150 locates at rear side of the curve mirror 130, and the plane mirror 140 (not shown in FIG. 2) locates at front side of the projection unit 110, the folding mirror 120, and the curve mirror 130 relative to the screen 150. In other words, the projection unit 110, the folding mirror 120, and the curve mirror 130 are disposed between the plane mirror 140 and the screen 150.
Because the conventional projection unit 110 is disposed between the plane mirror 140 and the screen 150, it may be necessary to take the throw ratio of the projection unit 110, which is defined as the ratio of the projecting distance to the image width, into consideration. For a desired image width, the bigger the throw ratio is, the longer the projecting distance will be required. In this situation, the greater spatial distance between the plane mirror 140 and the screen 150 is needed, for instance, increasing the heights of the plane mirror 140 and the screen 150 or increasing the spatial distance between the plane mirror 140 and the screen 150 to lengthen the projecting distance for obtaining a big enough image width. Whereas, the image width may not be big enough if both the heights of the plane mirror 140 and the screen 150 or the spatial distance between the plane mirror 140 and the screen 150 are constant. However, the increase of the projecting distance or the insufficiency of the image width is unacceptable because it is contradictory to the demand trend for thinner thickness and bigger area of the image display apparatus.
On the other hand, if another projection unit is used in the conventional inner projection TV 100, the design of optical paths among the projection unit 110, the folding mirror 120, the curve mirror 130, the plane mirror 140, and the screen 150 is altered. In other words, both the heights of the plane mirror 140 and the screen 150 or the spatial distance between the plane mirror 140 and the screen 150 should be readjusted accordingly. Therefore, if the projection unit 110 is disposed between the plane mirror 140 and screen 150, the selection of the projection unit 110 is limited to certain degree. In consequence, not only the design model option will be lack of flexibility but also the component configuration will become difficult.